Impedance Boundary Condition
The Impedance Boundary Condition provides a boundary condition that is useful at boundaries where the electromagnetic field penetrates only a short distance outside the boundary.
The boundary condition approximates this penetration to avoid the need to include another domain in the model. The material properties that appear in the equation are those for the conductive material excluded from the model.
The skin depth (that is, the distance where the electromagnetic field has decreased by a factor e−1) is for a good conductor
The impedance boundary condition is a valid approximation if the skin depth is small compared to the size of the conductor. The source electric field Es can be used to specify a source surface current on the boundary.
The impedance boundary condition is used on exterior boundaries representing the surface of a lossy domain. The shaded (lossy) region is not part of the model. The effective induced image currents are of reduced magnitude due to losses. Any current flowing into the boundary is perfectly balanced by induced surface currents as for the perfect electric conductor boundary condition. The tangential electric field is generally small but nonzero at the boundary.
The Harmonic Perturbation subnode (it is of the exclusive type) is available from the context menu (right-click the parent node) or on the Physics toolbar, click the Attributes menu and select Harmonic Perturbation. For more information see Harmonic Perturbation — Exclusive and Contributing Nodes in the COMSOL Multiphysics Reference Manual.
Use it to specify a perturbation source electric field.
Impedance Boundary Condition
The following material properties can be defined for the domain outside the boundary, which this boundary condition approximates. The default use the values From material. For User defined enter different values or expressions.
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Relative permittivity, εr (dimensionless)
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Relative permeability, μr (dimensionless)
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Electrical conductivity, σ (SI unit: S/m)
Based on space dimension, enter coordinate values or expressions for the Source electric field Es (SI unit: V/m).